NEC 2014, Table 310.15 (B) (16) (formally table 310.16)

[wawasworld]

in the 2008 NEC we have all used the Table 310.15 (B)(6) for sizing our service conductors for single phase dwelling services, (ie. 4/0 XHHW Alum for a 200amp service). Now in the 2014 NEC for a 200amp service we would need to bump to 250kcmil as per Table 310.15 (B)(16) (formally table 310.16), I did ask an inspector on this and he did not have an answer, I'm not sure where to size service conductors for single family dwellings in the 2014 NEC???? I feel that we should not need to bump our sire size to 250kcmil, I was wanting to see if anybody else has ran into any issues with this and what the results were, thanks for any input you can provide.

 

[charlie b]

You don't have to use table 310.B(15)(16), and you don't have to bump up the conductor size. You can still use the 4/0 aluminum XHHW. The new approach to sizing services and feeders to individual dwelling units is to find a conductor (your choice) that has an ampacity of at least 83% of the calculated service or feeder load. So if you want to serve a 200 amp load, you find a conductor with an ampacity (adjusted and corrected, if applicable) of 166 amps. A 4/0 aluminum XHHW has an ampacity of 180, so you can use it.

 

[Dennis Alwon]

I agree with Charlie. Basically the old table and the 83% are about the same however in the 2014 you will need to consider de-rating. For instance if you use ser cable thru insulation then you must use the 60C rating of the 4/0 al. Since 4/0 at 60C is only 150 amps then you would need to use 250 kcm al to satisfy the code at 200 amps

 

[ActionDave]

.....For instance if you use ser cable thru insulation then you must use the 60C rating of the 4/0 al. Since 4/0 at 60C is only 150 amps then you would need to use 250 kcm al to satisfy the code at 200 amps

That is just plain ridiculous. How much 4/0 is out there now just waiting to burst into flames?

Oh wait, none since it all seems to be holding up fine since the seventies and on through the millennium.

 

[kwired]

That is just plain ridiculous. How much 4/0 is out there now just waiting to burst into flames?

Oh wait, none since it all seems to be holding up fine since the seventies and on through the millennium.

Where it may make more sense though is in a multifamily application where several feeders are in a raceway, aux gutter, etc. 2011 you could have run every feeder through same wireway with no adjustments - just size to the table. 2014, still need same minimum size, but now need to apply adjustment factors just like where they are needed for other applications.

There are still going to be instances where it may not make any sense, just like before you could occasionally look at a particular application and ask why don't we need to adjust ampacity?

 

[1793]

I agree with Charlie. Basically the old table and the 83% are about the same however in the 2014 you will need to consider de-rating. For instance if you use ser cable thru insulation then you must use the 60C rating of the 4/0 al. Since 4/0 at 60C is only 150 amps then you would need to use 250 kcm al to satisfy the code at 200 amps

That's how it was explained to me when I brought it up during a Continuing Education class.